Unconventional component of parent materials of moldavites Jiří MIZERA, Zdeněk ŘANDA , Jan KAMENÍK

1. Unconventional component of parent materials of moldavites Jiří MIZERA, Zdeněk ŘANDA, Jan KAMENÍK Nuclear Physics Institute, Academy of Sciences of the Czech Republic Řež 130, 250 68, Czech Republic E-mail: mizera@ujf.cas.cz 3rd International Nuclear Chemistry Congress Sicily – Italy 18 - 23 September 2011 Summary Formation of the Central European tektites - moldavites - has unequivocally been associated with a large meteorite impact to Ries region in western Bavaria in Germany 14.5 million years ago. However, after several decades of investigation, unambiguous assigning all source materials of moldavites and processes of their chemical differentiation still remains open. Despite some similarity of chemical composition between moldavites and isochronous sediments from vicinity of the Ries crater, there are some significant differences in both major and trace element contents, which cannot be attributed solely to the variability of the sediments or later weathering processes. Some of these differences could be explained by an original hypothesis, according to which ash from biomass burned at the early stage of the meteorite impact contributed to the source materials. Geochemical characterization of a large collection of moldavites using instrumental neutron/photon activation analyses supported the hypothesis. As shown by the data acquired in the study, this unconventional “biogenic component” could be indicated by enrichment in elements essential for plants (e.g., K, Ca, Mg) and depletion of nonessential elements (e.g., Na, Rb, Sr, Ba), similarly to redistribution of these elements during their transfer from soil to plants. Differentiation similar to that occurring during the soil-plant interaction has been observed also for other, nonessential elements, e.g., U and Th. Correlations between the K/Na ratio and K/Rb, Ca/Sr, Ca/Ba, and U/Th ratios, as well as some other indicators of the “biogenic” component observed in moldavites from various parts of the Central European tektite strewn field are presented and discussed. Moldavites from Southern Bohemia. Central European tektite strewn field and its substrewn fields. • Experimental • collection of 103 moldavites from the major parts of the Central European tektite strewn field: Southern Bohemia (MSB, 59), Cheb Basin (MCB, 30), Moravia (MM, 13), Lusatia (ML, 1) • analyzed by INAA and IPAA using the LVR-15 reactor of the Nuclear Research Inst., Řež, plc., and the MT-25 microtron of the Nuclear Physics Inst. ASCR, respectively • selective irradiation with epithermal/fast neutrons in Cd shielding included – interferences from fission suppressed (95Zr, 99Mo, 140La, 141Ce, 147Nd) • various irradiation - decay - counting modes applied • RM used for QC: USGS GSP-1 granodiorite, SARM GS-N granite * - counting with planar HPGe detector Results In plants, due to enrichment in essential elements and depletion of nonessential elements, besides K/Na also Si/Al, Ca/Al, K/Rb, Ca/Sr, and Ca/Ba ratios increase during transfer of the elements from soil to plants.Redistribution of some nonessential elements as U and Th also occurs by soil-plant interaction. Significant correlations between these ratios observed in moldavites might thus be an indicator of the “biogenic” component in the parent materials of moldavites. The current concept of moldavite parent materials assumes mixing of 3 components of the Miocene sediments - quartz sands, clayey soil, and a Ca-Mg component.The Ca-Mg component has newly been assigned (besides carbonates) to ash produced from burnedbiomass and soil during the meteoritic impact. Composition of plant ash is governed by Ca, Si, K, Mg, and Mn, and characterized by a high K/Na ratio. Correlations between the K/Na ratio and the major elements support this assignment, particularly in a part of the Cheb Basin moldavites. The study has been supported by the Czech Science Foundation grant 205/09/0991.